There is only one modern species of sperm whale, but it’s a family that was more diverse in the past. A big question for paleontologists is “just how diverse”, because sperm whales are rare in the fossil record. The most common remains are teeth, but unfortunately sperm whale genera cannot be reliably identified based on teeth alone.
That doesn’t mean that the teeth are completely useless for identification. The uppermost bed of the Calvert Formation includes at least two species of sperm whales, based on the types of teeth that have been found.
In the photo above, the tooth on the right is from the Rappahannock sperm whale that I’ve been writing about recently. This is from a very large whale, comparable in size to the baleen whales from the same formation.
The tooth on the left is from the same bed, but from Carmel Church. Besides the rather obvious size difference, the teeth differ in that the small one has no enamel crown. Small-toothed sperm whale skulls (generally referred to as Orycterocetus) have been found lower down in the Calvert Formation.
So, even with teeth alone, we can say definitively that there were at least two sperm whales in the upper Calvert Formation, even if we can’t be 100% sure what those two species are.